The corneal reflex (or in another way, corneal, blinking, conjunctival) is a natural reaction of the body to irritation of the cornea of the eyes. Checking for its absence or attenuation serves as an auxiliary diagnostic sign of some pathologies. The corneal reflex also allows you to assess the degree of immersion in anesthesia.
general description
The cornea of the human eye and other animals is highly sensitive. This is due to the fact that around it there is a nerve plexus of long ciliary nerves. In the cornea, they do not have a myelin sheath, and therefore they become invisible.
There are 3 levels of nerve weave. The closer the nerves are to the corneal surface, the thinner and thicker they are. Almost every cell of the outer layer of the cornea has a separate nerve ending. Therefore, a person experiences a pronounced pain syndrome with mechanical irritation of this area, as well as with its inflammatory diseases.
High sensitivity of the cornea is one of the natural protective mechanisms of the organs of vision. The corneal corneal reflex is especially pronounced in newborn children. After 1 year of life, it gradually weakens. In adults, in isolated cases, it may not be detected at all.
What is it manifested in?
The corneal reflex manifests itself in the form of the following process:
- eyelids close;
- the eyeball turns up, removing the cornea under the eyelids;
- lacrimal glands secrete a fluid that washes away irritating particles.
Reflex can occur with a light touch of the cornea or even with the movement of air, a sharp increase in illumination, with the rapid approach of an object to the eye, or as a result of a reaction to a sudden strong sound.
Kinds
The corneal reflex can be divided into 2 categories:
- corneal, caused by irritation of the cornea;
- conjunctival (conjunctival) - when exposed to the conjunctiva.
The latter is often absent in healthy people.
The trigeminal nerve performs the sensitive part of the reflex arc, and the facial nerve performs the motor part.
Diseases
Loss or weakening of the corneal migratory reflex is observed in the following conditions:
- severe brain injuries (in particular in its stem part), accompanied by a coma;
- damage to the cervical vertebrae;
- swelling of the auditory nerve, while the patient also has unilateral hearing impairment and impaired swallowing;
- organic lesion of the trigeminal, facial nerve;
- pathological changes in the cornea of the eye;
- deformation of the Varolian bridge, responsible for the transmission of impulses from the spinal cord to the brain.
Reflex can also fade away with hysteria, especially on the side of the face where skin loss occurs.
Corneal reflex research
The procedure for checking the reaction of the eye is performed in the following order:
- the patient is laid on a couch in a horizontal position;
- raise the upper eyelid to widen the palpebral fissure;
- touch a piece of sterile cotton to the cornea.
If the eyeball "rolled", and the eyelids closed, then the reflex is not broken, and vice versa. In patients who are in an unconscious state, the study is carried out similarly. Sometimes, for such patients, a check is made using a thin stream of water.
The intensity of the corneal reflex, as for other tests conducted on the mucous membranes, varies widely.
The effect of drugs and other substances
A decrease in this reflex occurs not only with traumatic brain injuries and diseases of the central nervous system, but also with the use of certain medications. These include the following:
- sedatives;
- barbituric acid derivatives;
- painkillers;
- antipsychotic;
- anticonvulsants;
- antiemetic;
- drugs for the treatment of Parkinson's disease.
Violation of the normal reaction of the cornea is also observed with abuse of alcoholic beverages and with an overdose of narcotic substances.
A corneal reflex occurs in patients who use contact lenses for the eyes. The cornea perceives them as a foreign body, so unpleasant sensations appear. However, this does not mean that you will have to abandon this effective method of vision correction. In order to get used to the lenses, doctors recommend “training” the eyes a few weeks before the start of their use by touching them with a piece of sterile cotton wool. Before doing this, wash your hands thoroughly so as not to cause infection.
Importance in Medical Diagnostics
Inhibition of the corneal reflex may indicate that the patient fell into a coma. If the reflex weakened gradually, then this makes it possible to suspect the presence of internal hemorrhage in the brain, in which the lesion area increases in size over time. Conversely, if the reflex suddenly reappears, then this indicates an improvement in the condition of a person after a traumatic brain injury.
However, this symptom cannot serve as the sole diagnostic criterion. It is auxiliary in a comprehensive examination of the patient.
The study of the corneal reflex helps not only to identify certain pathologies, but also serves to determine the degree of immersion of a person in general anesthesia before surgery.
After administering an anesthetic, the doctor always checks the reaction of the cornea of the eye. If it is absent, this means that the drug has reached the brain stem, and the patient will not feel pain during surgical procedures.